U.S. patent number 6,155,160 [Application Number 09/325,361] was granted by the patent office on 2000-12-05 for propane detector system.
Invention is credited to Kenneth Hochbrueckner.
United States Patent |
6,155,160 |
Hochbrueckner |
December 5, 2000 |
Propane detector system
Abstract
An electronic control for a grill, providing enhanced
functionality and safety features. A hydrocarbon detector system
provides an intermittently operated electro-optic device emitting
photons at a wavelength which selective interacts with hydrocarbon
as compared to air, associated with a detector for detecting the
selective interaction and an alarm monitor for detecting an alarm
state. A food temperature sensor is employed to proportionately
control combustible fuel flow rate, to thereby control a food
temperature profile. A communications network interface is provided
to allow remote control and monitoring.
Inventors: |
Hochbrueckner; Kenneth
(Richmond Hill, NY) |
Family
ID: |
26777548 |
Appl.
No.: |
09/325,361 |
Filed: |
June 4, 1999 |
Current U.S.
Class: |
99/331; 126/112;
126/39R; 126/41R; 250/339.04; 250/343; 340/632; 99/337; 99/342;
99/344 |
Current CPC
Class: |
G05D
23/1917 (20130101) |
Current International
Class: |
G05D
23/19 (20060101); A23L 001/00 (); G01N 007/00 ();
G01N 021/61 () |
Field of
Search: |
;99/325-333,337,338,342-344,400,401,444-450 ;73/23.2,31.05
;122/448.1,504 ;126/112,39R,41R,116
;250/343,351,339,345,339.13,339.04,43.5,338.5 ;307/118,140,683
;340/632,634,628-630 ;422/90,98,83,88 ;431/76,22 ;432/36 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simone; Timothy F.
Attorney, Agent or Firm: Milde, Hoffberg & Macklin,
LLP
Parent Case Text
This application claims the benefit of U.S. provisional application
No. 66/087,946, filed on Jun. 4, 1998.
Claims
What is claimed is:
1. An electronic control system, comprising:
(a) a microcontroller;
(b) a telecommunications network interface, controlled by said
microcontroller; and
(c) a condition detector, producing an output received by said
microcontroller;
said telecommunications network interface having a low latency
communications mode and a high latency communications mode, wherein
said communications mode is controlled by said microcontroller.
2. The electronic control system according to claim 1, further
comprising:
a user input, for receiving a user desired end cooking state;
said detector being a food temperature sensor; and
a combustible cooking fuel combustion rate output;
wherein said microcontroller proportionally controls said
combustible cooking fuel combustion rate output responsive to said
input from said food temperature sensor and said user input, and
produces a cooking complete signal when said desired end cooking
state is achieved.
3. The control system according to claim 1, further comprising a
combustible gas detector, for detecting a presence of combustible
gasses, providing an input to said microcontroller, said
microcontroller producing an alert in an event of combustible
gasses exceeding a threshold.
4. The control system according to claim 3, wherein said
combustible gas detector comprises:
(a) an electro-optic device emitting photons at a wavelength which
selective interacts with a hydrocarbon as compared to air,
associated with a detector for detecting the selective interaction;
and
(b) an alarm monitor for receiving an output of said detector when
said electro-optic device is activated and determining a
relationship of a detected hydrocarbon level and a predetermined
value.
5. The control system according to claim 1, further comprising a
partial combustion product detector, for detecting a presence of
gaseous partial combustion products.
6. The control system according to claim 2, wherein said food
temperature sensor provides said input to said microcontroller
wirelessly.
7. The control system according to claim 2, wherein said food
temperature sensor determines a temperature of at least two
portions of the food.
8. The control system according to claim 2, further comprising a
remote user interface communicating through the telecommunications
network interface wirelessly.
9. The control system according to claim 2, further comprising a
proportional fuel control valve.
10. The control system according to claim 1, wherein the
telecommunications network interface comprises a wireless switched
packet network communicating with a remote terminal.
11. The control system according to claim 1, wherein said
telecommunications network interface communicates with a packet
switched communications network.
12. The control system according to claim 1, wherein said condition
detector is selected from one or more of the group consisting of a
combustible gas detector and a toxic gas detector.
13. The control system according to claim 1, wherein said detector
comprises an optical hydrocarbon detector.
14. The control system according to claim 12, wherein said detector
operates intermittently.
15. The control system according to claim 1, further comprising a
food temperature sensor.
16. The control system according to claim 15, wherein said food
temperature sensor operates wirelessly.
17. The control system according to claim 1, further comprising a
combustible fuel remaining input to said microcontroller.
18. The control system according to claim 1, wherein said detector
is associated with a propane grill.
19. The electronic control system according to claim 1, wherein
said detector comprises:
(a) an electro-optic device emitting photons at a wavelength which
selective interacts with a hydrocarbon as compared to air,
associated with a detector for detecting the selective
interaction;
(b) a system power controller to activate said electro-optic device
intermittently at a duty cycle of less than about 25%; and
(c) an alarm monitor for receiving an output of said detector when
said electro-optic device is activated and determining a
relationship of a detected hydrocarbon level and a predetermined
value.
20. The control system according to claim 19, wherein said
electro-optic device comprises an infrared light emitting diode
device.
Description
FIELD OF THE INVENTION
The present invention relates to the field of safety devices, and
more particularly to propane detector systems for use in
conjunction with domestic propane tanks. Compressed combustible gas
tanks pose a potentially serious hazard, which can be ameliorated
by detecting leakage before the gas reaches an explosive
concentration.
BACKGROUND OF THE INVENTION
Compressed propane is often used as a convenient heating and
cooking fuel. It can be transported in refillable tanks, or
delivered by truck to stationary tanks. In many instances, the
necessary valves and couplings pose a potential leakage hazard. If
leakage is sufficient, propane gas, which is heavier than air, can
accumulate and mix with the air, forming an explosive mixture. A
propane tank must not be filled above capacity, normally 80% of
volume, in order to accommodate thermal expansion of the gas and
liquid in the tank. Approved tanks each include a pressure relief
valve, which allows escape of propane in the event of overfilling,
avoiding the risk of rupture of the tank with release of all of the
propane. However, these relief valves themselves release propane
into the atmosphere, which may reach dangerous levels. The risk of
overfilling is increased in the case of transportable propane
tanks, e.g., D.O.T. approved 20 lb. tanks. There therefore remains
a need for a system to detect propane leakage around propane tanks,
to provide an alert of the potential hazard.
A large number of explosive gas detectors and propane detectors are
known. Available types, fall into four general categories:
1. calorimetric analysis of sample gas
2. photometric analysis of sample gas
3. semiconductor detectors
4. laboratory, chemical and other detectors
A calorimetric detector seeks to determine the functional presence
of combustible gasses by oxidizing any such gases present, and
measuring the "excess heat" generated. These detectors, for
example, employ a heated catalytic bead and non-catalytic head
disposed on legs of a platinum resistance thermometer, measuring
the differential bridge voltage due to the flammable gas induced
heating of the catalytic bead with respect to the non-catalytic
bead. New technologies allow micromachined devices to serve as
combustible gas detectors, for example so-called microcanteliever
devices developed by Oak Ridge National Labs.
A photometric gas detector seeks to detect the presence of gas by a
signature pattern, for example the spectrographic characteristics
of the gas. Typically, the characteristic absorption peaks of
hydrocarbon gasses fall in the infrared range. The photometric
characteristics of a gas may be measured locally, in a detector
space, or remotely, such as by remote laser sensing techniques.
A semiconductor detector operates by selectively or semiselectively
absorbing the gas to be measured to a semiconducting material, and
measuring an alteration in the conductive properties of the
semiconducting material. Typical semiconductors include tin oxide,
lathough a number of other semiconducting materials may also be
used. Semiconducting detectors typically have low selectivity, and
respond to a broad range of gasses, for example lower hydrocarbons
and alcohols, carbon monoxide, hydrogen sulfide, and other
gasses.
Lastly, there are a number of specialty detectors, for example
those used in laboratory analyses, color change detectors, mass
spectroscopy, and the like, which may also detect gasses.
In a domestic environment, propane gas is used to provide heat, for
cooking, and for barbecues. While some types of detectors are
available which will detect leaking propane, their use is limited,
especially in uncontrolled environments. Thus, the available
domestic flammable gas detectors are intended for permanent
mounting, continuous operation and line current operation.
Propane tanks for domestic barbecues are typically refilled and
transported. U.S. Department of Transportation (D.O.T.) regulations
carefully describe the construction and features of these tanks, in
order to ensure safe transport. These tanks are each provided with
a safety relief valve, near the main valve, which vents in the
event of overpressure. Propane tanks for barbecues are
approximately 18" high and 12" diameter, with a valve system
centered on the top surrounded by a handle/protective cage about
270.degree.. The valve handle extends upward, below the upper
extent of the handle/protective cage, and has a nozzle which
projects at right angles toward the open portion of the
handle/protective cage. The handle/protective cage has three
openings, a larger of which serves as a handle. The base of the
tank includes a conic section between a spherical lower portion of
the tank and the ground.
Typically, the sensing system used in distributed combustible gas
detectors includes an electronic sensor detecting the presence of
combustible gas, such as a heated sensor with a flame arrestor,
forming an "intrinsically safe" module (i.e., low probability that
the detector may itself ignite the propane). An alternate type of
sensing system employs a semiconductor which responds to the
presence of various Lyases, such as propane. For example, Motorola
Senseon MGS-1200 sensor, Figaro TGS2612, Figaro TGS 813, English
Electric Valve (EEV) heated catalytic bead combustible gas sensor,
or similar types may be used.
Carbon monoxide is a normal product of propane combustion, and in
closed environments, this may also become a hazard. Known carbon
monoxide sensors include the Figaro TGS2440. Figaro TGS800 and
Motorola Senseon MGS-1100. The later two sensors have marked cross
sensitivity with propane, and thus may be used to detect both
hazards, but cannot alone distinguish them. Carbon monoxide is
typically sensed with semiconductor-type sensors or electrochemical
detectors.
As a result of the permissible characteristics, including allowable
power consumption, warm-up time and other constraints, installed
domestic sensors can easily employ sensors with moderate or high
current consumption, long warm-up stabilization time and bulky
size. Known portable personal safety devices also employ these
types of sensors: however the systems provide a limited battery
life and may be relatively heavy due to the batteries necessary to
run the integral sensor heaters.
Heated sensors, such as the Senseon series of gas detectors, are
micromachined and employ an element covered with a catalytic
material, which is electrically heated. For example, a Senseon MGS
1200 type device employs a tin oxide film. The temperature of the
sensor is measured, for example as compared to a like sensor
element absent the catalyst.
These semiconductor sensors may also be used to detect combustible
gasses. In the MGS 1200, propane interacts with the heated catalyst
to alter its conductivity. In other systems, the degree of
temperature rise of the catalytic element is related to the amount
(caloric content) of combustible gas present.
Catalytic and semiconductor sensors may require long stabilization
times, in order to eliminate non-specific absorption to the
catalyst or other interfering influences.
Thus, The following U.S. Patents, as well as references cited
therein, incorporate herein by reference, relate to gas detection
and associated technologies: U.S. Pat. Nos. 5,879,631; 5,828,307;
5,807,098; 5,797,358; 5,709,222; 5,650,024; 5,379,026; 4,709,150;
4.437,005; 4,323,777; 5,721,430; 3,662,171; 5,444,249; 5,608,219;
5,070,244; 5,464,983; 4,916,437; 4,694,174; 4,560,875; 5,475,222;
3,861,809; 5,026,992; 4,647,777; 4,567,366; 4,958,076; 4,500,207;
4,899,053; 4,489,239; 4,871,916; 4,853,543; 5,637,872; 5,372,785:
5,250,170; 4,580,439; 5,012,671; 5,003,812; 4,164,539; 5,218,347;
and 4,614,669.
U.S. Pat. No. 5,813,394, expressly incorporated herein by
reference, relates to a cooking grill with a flame detector, for
relighting the flame if blown out and providing automatic
shutoff.
SUMMARY OF THE INVENTION
The present invention provides a combustible gas detector system
for use in domestic environments, and in particular proximate to
propane tanks.
The detector system has low power consumption, and is suitable for
extended operation in relatively unprotected environments. In pulse
operation mode, a preferred embodiment has a short stabilization
time, allowing substantial power savings over a continuous
operation system. Thus, the system may be used in remote locations
with low maintenance.
Typically, propane tanks are housed outdoors, or in non-enclosed
environments. This is because, in the event of a leak, an explosive
mixture easily forms with air which can result in catastrophic
explosions. Propane gas is dense, and therefore does not dissipate
easily. Thus, effective flammable gas detectors must be located
near the tank and/or below it.
Even when stored in the open, gas leaks are hazardous. However,
heretofore no system has been designed to particularly address
detecting the hazards of domestic propane storage.
The present invention therefore provides a detector suitable for
battery operation over extended periods, which accurately detects
propane leakage with high sensitivity and specificity, preferably
without substantial susceptibility to false positive alarms and
which does not itself present an explosion hazard in the event of
leakage. In order to provide prolonged battery operation, portions
of the device are preferably powered intermittently, employing a
sensor which requires a short settling (stabilization) time for
accurate measurements.
The preferred detection technology is a photometric detector, and
more particularly a detector detecting the presence of gasses
having a specific characteristic absorption of infrared light at
one or more wavelengths in the bands 3000-2700 cm.sup.31 1 and/or
1475-1300 cm.sup.31 1. These wavelengths are relatively specific
for the C--H bond stretch and bend, respectively.
In detecting this absorption, a narrowband infrared light emitting
semiconductor structure, such as a light emitting diode or laser
diode, may be used. Alternately, a filtered broadband light source
or narrowband detector may be used. The most common interfering
gasses are carbon dioxide, carbon monoxide and other combustion
products, which may be the result of the normal use (combustion) of
the propane. One option is to provide non-selective detection of
multiple potential hazards simultaneously. Alternately, the sensor
or multiple sensors may be operated to distinguish the various
gasses.
In a preferred embodiment, propane is detected optically. An
optical absorption (or other wavelength specific photon
interaction) of a gas sample is detected at at least a first
wavelength wherein the gas of interest has a specific absorption,
preferably at an absorption maxima or at a wavelength which best
distinguishes the gas of interest from potentially interfering
gasses. In order to compensate for detector baseline drift and
offset, changes in sensitivity, temperature variations, and the
like, a second optical absorption (or other wavelength specific
photon interaction) of a gas sample under similar circumstances to
the first measurement is obtained, at an optical wavelength which
has a different optical characteristic, preferably a low specific
optical absorption. For example, a single silicon detector is
illuminated by two infrared light emitting diodes, one having a
wavelength corresponding to a peak absorption or propane and
another corresponding to low absorption by air and/or air mixed
with propane. The differential output from the two illumination
conditions for normal air is stored as an offset, and measurements
of sample gas taken intermittently thereafter. Since the
sensitivity of a temperature compensated detector is likely less
sensitive to environmental variations and stabilization time than
the offset, this technique will allow relatively long periods
between samples, prolonging battery life. Intermittent in this case
means, for example, a duty cycle of 0.1% or 0.01%, with short
measurements taken every 0.5 to 5 minutes. In order to compensate
for gain drift, cuvettes of clean air and known sample gas may be
selectively disposed along the optical path (e.g., by repositioning
a mirror, or providing two nearly identical optical sources and a
single detector), with the differential between the two used to
calibrate the detector for an unknown sample. In known manner,
multiple wavelength measurements may be provided for increased
detector performance.
U.S. Pat. No. 5,822,058, expressly incorporated herein by
reference, discloses an optical spectrometric system for
measurement of hydrocarbon fuel gas in a supply line. This
technology may also be adapted for measurement of dilute propane
and other combustible gasses according to the present invention.
U.S. Pat. No. 5,793,295, expressly incorporated herein by
reference, also discloses an optical gas detection system which may
be useful as a part of, or in conjunction with other elements
according to the present invention.
U.S. Pat. No. 5,753,797, expressly incorporated herein by
reference, relates to a photoacoustic gas sensor adapted for
detecting combustible gasses including concentrations which pose an
explosive hazard.
Thus, a key feature according to a preferred embodiment of the
present invention is that the sensor has low sensitivity to
temperature variations, or these variations may be predicted and
compensated. Thus, the optical system may reach operating
conditions immediately or after a very short warm-up time. As
necessary, real-time calibration or differential measurements may
be used to maintain system accuracy.
In this manner, the system may operate analogously to known smoke
detectors. which intermittently seek to detect increased optical
absorption from smoke particles or the presence of ionizable
particles in the air. By providing a duty cycle of less than 0.1%.
battery life of months or years may be obtained from a single
commercially available battery, e.g., a 9V transistor-type
battery.
Laser diodes hold promise as intrinsic gas detectors because the
presence of an absorptive gas in the laser cavity may alter a
lasing threshold, produce a measurable fluorescence, or allow
wavelength specific absorption measurements. Thus, one embodiment
provides an integrated optical detector which includes a resonant
laser cavity having an air space, through which sample gas passes
or a special detector surface which has optical properties which
alter in response to a propane concentration in a gas space. The
laser has a mode which corresponds to an excitation wavelength or
absorption peak of propane. Therefore, the laser resonance,
especially the startup transient, will be altered by the presence
of propane in the gas space. By analyzing the transient or
absorption, the amount of propane may be determined accurately. In
a related embodiment, the propane itself may form part of a laser
system. In this case, the detection may employ one or more optical
wavelengths. It should be understood that ion various embodiments,
the propane may either extinguish the laser resonance or increase
it, in the manner of a laser dye.
While the static characteristics of the electro-optical system may
be measured, this is not preferred for two reasons. First, the
static operation measurements typically require the component to be
powered for a longer period of time, hence drawing more power, and
second the optical excitation may itself alter the propane
concentration in the gas.
Advantageously, the detector according to the present invention is
physically associated with a propane tank, for example, being
located on or in a cover thereof. This proximity increases the
concentration of propane present at the detector in the event of
leakage from the tank, thus lowering the required inherent
sensitivity for reliable operation. In addition, it is generally
desirable that the sensor detect the highest local concentration of
combustible gas, in order to best judge the explosive hazard. The
cover, for example may be a polyvinyl chloride sheet that is
fabricated to conform the upper exterior profile of a portable
tank, such as is used for barbecues.
In a barbecue environment, the gas detector system may be
integrated into a more complex multifunctional system. This system
detects combustible gasses, producing an alert if above a threshold
level, for example due to valve leakage, mechanical defect, or
overpressure relief. The alarm will also alert the user of a flame
out or non-start condition of the barbecue. In the later case, it
might be hazardous to ignite the propane if the environment is
flooded with gas in explosive proportions.
The system may also include sensors for remaining propane level,
barbecue temperature, food temperature, and other data. An audio
transducer near the propane tank valve may be monitored for
turbulent noise, indicative of barbecue operation.
Inadequately cooked foods are a known health hazard. On the other
hand, overcooked foods on a grill may contain excess quantities of
potential carcinogens, reduced nutritional value, and impaired
taste and texture. Therefore, it is desired to optimize the cooking
time and temperature of foods on a grill. By providing an
intelligent electronic system, food core temperature may be
monitored to determine cooking status, and provide an indication
thereof to the chef. These may be wired temperature sensors, such
as thermistors or semiconductor diodes, or even wireless
transponders that relay temperature to an electronic interrogation
system. A wireless transponder may be, for example, a surface
acoustic wave device or active semiconductor device. The
temperature sensor is, for example, inserted in the middle or core
of the food. Advantageously, a more complex sensor may be provided
to detect a temperature profile through the food. For example, it
is desired that the core temperature of "well done" meat be at a
certain minimum temperature, while the periphery should not be
burnt. Therefore, by detecting the temperature profile, the cooking
temperature as well as time may be controlled and optimized to the
cooking preferences of the individual, and to compensate for
variations in cooking conditions across the grill.
The sensor system preferably has audible and visible alarms. For
example, the audible alarm is a piezo-electric transducer, driven
near a resonant frequency with a modulated waveform. The visible
alarm is, for example, a high brightness LED.
A particularly hazardous product of propane combustion is carbon
monoxide. While normally this dissipates, when operated indoors or
under poor ventilation, a hazardous amount may be present.
Therefore, a carbon monoxide detector may also be integrated with
the propane detector to detect and warn of this condition. While
the cross sensitivity of a sensor may be exploited to detect both
hydrocarbons and carbon monoxide, the differential sensitivity is
not easily controlled, and therefore the respective alarm levels
may be inappropriate. In addition, the "normal" carbon monoxide
level will vary depending on whether the barbecue is in operation
and the proximity and orientation of the detector to the
burner.
Advantageously, therefore, where the primary hydrocarbon sensor has
cross sensitivity to carbon monoxide, an auxiliary sensor, such as
an electrochemical sensor (cyclic voltammetry or static potential
reducing species detector) or semiconductor sensor may be provided
to differentiate the carbon monoxide from the hydrocarbon. In
another embodiment, when the optical detector detects an abnormal
condition, a secondary, and more power consuming sensor, is
activated to make a second, more selective, measurement.
In another embodiment, the sensor detects whether a flame is
present in the burner, and adjusts its mode of operation
accordingly; where there is no flame, the system operates at high
sensitivity to detect gas leakage, and in the presence of a flame
sensitivity is lowered to allow normal operation without alarm
ennuciation.
Advantageously, an electronic detector system may also encompass a
tank level gage as well. In this case, a set of temperature
sensors, for example silicon bipolar devices (e.g., diodes or
transistors), thermistors, thermocouples, or the like, are provided
in a vertical arrangement near the wall of the tank. As the propane
is used, the liquid propane in the tank will self-cool, forming a
temperature transition line at the liquid/gas interface within the
tank. A series of discrete sensors, or a single sensor strip may
also be provided which changes in characteristics at the
temperature change point, arranged vertically along the wall of the
tank, may be used.
In order to indicate the level, a visible indicator, for example an
LCD (liquid crystal display) bar graph display, may be provided in
the electronic system, which typically is nested next to the valve
and protected by the protective rim of the tank.
A set of visual indictors, for example pulse width or selectively
modulated LEDs, may be provided on a vertical strip, for example
adjacent to the sensors, which are illuminated to indicate the
liquid level in the tank. For example, a piezo electric transducer,
possible the same element as an audio alarm, is employed as a
microphone. When a sound having particular characteristics is
sensed, for example a clap, whistle, voice, or the like, the LED's
may be illuminated for a period, for example with a 2% duty cycle,
30 Hz repetition for about one half a second. The pulsing of the
LEDs is advantageous in that it improves the efficiency of LED
driving from a 3V (or higher voltage) battery and provides improved
perception, while limiting power draw. The LED's may be bicolor
LED's, e.g., red and greens with those above the level red, those
below the level red, and that at the level yellow (bipolar
excitation). Alternately, the one LED at the level may be
illuminated or those below the level illuminated. These functions
are typically defined in the software of a microcontroller which
controls the electronic system.
According to a different embodiment, tile level gage operates by
other than temperature change height. For example, an active
transducer may be used to measure the thermal capacitance of the
tank wall, which changes at the liquid height. Thus, a set of small
constant power heaters are provided which heat the wall by a small
amount, e.g., about 2.degree. C. The time to heat or relaxation
time to the ambient temperature is measured. The liquid will cool
the wall faster than the gas above the liquid-gas interface.
An acoustic sensor or acoustic sensor array may be used to produce
acoustic waves, which characteristically differ based on the liquid
level. For example, one or more piezoelectric elements rest against
the tank wall. One or more elements of the array are excited, for
example in a pulse or chirp waveform, and one or more of the
piezoelectric sensors is monitored for a received acoustic
waveform. Due to the differences in the acoustic properties of the
liquid with respect to the gas, the sensors will have outputs which
distinguish a liquid level. Alternately, an acoustic transducer
excites wave in the wall of the tank, which travels down the side
the tank. At the liquid level, an impedance mismatch occurs and a
portion of the wave is reflected. The characteristic timing of the
reflection is determined, as is well known in the field of time
domain reflectometry. The sensor control may be, for example, an
adaptive control, and thus need not be separately calibrated for
every tank.
In one embodiment, the electronic systems include a networking
device, for example a TCP/IP based communications interface, for
communicating with other devices in tile environment, or remotely.
For example, the microprocessor may include a so-called embedded
"web server" to communicate sensed conditions and to respond to
received commands or requests for information. Of course, the
controller need not itself implement these protocols, and may
communicate with a translation or bridge device using another
protocol. Therefore, the device may be integrated with other
domestic electronics systems and communicate therewith. Various
known physical link layers may be employed, such as 10 Base T, 10
Base 2, phone-line networking, AC power line networking, RF
communications (e.g., 24 MHz, 49 MHz, 900 MHz or 2.4 GHz), infrared
communications (e.g., IRdA), acoustic communications, or the like.
In order to reduce power consumption, a wireless communication
system preferably provides at least two modes of operation, an
active mode wherein the communications latencies are short, and a
low power mode wherein the communications are shut down or operated
with long latencies. The system may switch between modes
automatically or on external command.
As stated above, the combustible gas sensor is preferably an
infrared optical absorption sensor. This sensor detects a specific
characteristic absorption of infrared light at one or more
wavelengths in the bands 3000-2700 cm.sup.-1 and/or 1475-1300
cm.sup.-1. These wavelengths are relatively specific for the C--H
bond stretch and bend, respectively. While these bands do have a
number of possibilities for interference, the occurrence of such
interferences are not normally occurring, and an alarm condition
caused by the presence of interfering compositions would not defeat
the usefulness of the system. Further, the detection system
according to the present invention is intended to detect relatively
high concentrations of hydrocarbons, so slight interference can
typically be tolerated.
In order to detect these wavelengths, an infrared detector is
employed. Typically, these detectors have an output which varies
with temperature, and perform better (have higher signal to noise
ratio) at reduced (sub-ambient) temperatures. However, a number of
known methods may be employed to achieve adequate sensitivity at
ambient and uncontrolled temperatures.
It is understood that there are two theories for setting a
detection threshold for propane. The first deals with the explosive
hazard. In order for propane to cause an explosive hazard, it must
be present in excess of the lower explosive limit, about 3-4%. In
order to provide a safe margin, a threshold may be set at 25% of
lower explosive limit, or about 1%, which translates to 10,000 ppm,
clearly a substantial concentration. The detector according to the
present invention is typically directed toward the detection of
explosive hazards. The detector may also be useful for detecting
leaks, which in and of themselves may not pose an explosion hazard,
but are nevertheless undesired. Since propane use may normally lead
to some atmospheric leakage, the threshold must be set above
background and contamination levels, for example 100-500 ppm. Of
course, the measurements must be taken at an appropriate location,
and since propane is normally denser than air, the sensor should be
in a dependent location from the storage tank and hoses for maximum
reliability.
The irradiation source of the optical sensor may be a broadband
source, such as an incandescent bulb, or a narrow band emission
source, such as a light emitting diode or semiconductor laser,
e.g., in the 1475-1300 cm.sup.-1 band. Preferably, the system
operates as a differential infrared absorption detector, for
example with a first measurement at 1300 cm.sup.-1 and a second
measurement at 1425 cm.sup.-1, employing a single detector and two
excitation sources, e.g., a broadband source with a pair of
narrow-band optical filters, for example operating in an optical
chopper configuration, two light emitting diodes at different
wavelengths. Alternately, a reference gas and sample gas form the
basis for the two measurements with simultaneous or sequential
measurement of optical absorption.
Alternately, a wavelength sweeping irradiation source may be used.
Typically, such sources employ a broadband source with a
diffraction grating filter. However, such devices are generally
more costly than desired for a system according to the present
invention. Therefore, the wavelength shift on warming up, such as
(generated in light emitting, (diodes, may be used to excite the
detector. For example, an infrared light emitting diode at ambient
temperature (20.degree. C.) has a wavelength of 1400 cm.sup.-1.
When warmed, for example by pulsing a current of 30 mA for a short
period, the diode may be heated to 65.degree. C. or higher. At this
temperature, the output wavelength in creases, for example to 1425
cm.sup.-1. Since propane (or other hydrocarbons) have a high
extinction coefficient in this range, any significant differential
absorption, as measured by a change in detector output, would
indicate the presence of such a gas. Thus, a usable system is
provided by operating an infrared diode in pulse operation,
detecting a differential signal as the diode is heated. The
requirement that the diode cool between readings is not a
disadvantage, since the system is intended to operate
intermittently to conserve battery power.
In any case, the infrared absorption or differential infrared
absorption is detected, and compared to an alarm threshold reading.
The processor may also implement a so-called adaptive baseline, to
correct for normal variations in the characteristics of the system
over time and varying environmental conditions. In this case, the
system presumes that hazardous conditions tend to occur quickly,
for example over minutes, while baseline shifts occur slowly, over
hours. Therefore, slowly varying signals are subtracted from the
reading, so rapid changes are more readily detected. Of course, the
system is preferably separately temperature compensated, because
temperature changes may occur rapidly, for example due to changing
shadows and the local heating from operation of a barbecue.
The system may also be calibrated by the use of a propane source,
and so-called "zero gas", a known contaminant-free gas supply. This
zero gas may, for example, be approximated by electrolytic oxygen,
although quantities must be very limited to reduce fire or
explosion hazard from this process.
When a super-threshold concentration of hydrocarbon (propane) is
detected, an audible alarm is sounded and a visual alarm may be
projected. These alarms may become intermittent after a period, to
avoid wasting the remaining battery power if there is no action
taken to silence it. A battery life detector is also preferably
integrated in the system and determined with each measurement.
A carbon monoxide sensor may be provided which is, for example,
also an infrared sensor, for example in the 1900-1650 cm.sup.-1
band, or a semiconductive sensor which selectively changes
impedance with carbon monoxide concentration, such as a Senseon
MOIGS 1100 type device.
An acoustic sensor, such as a microphone or piezoelectric element
may be provided to determine whether the propane tank is in use or
not, a use condition generally being associated with some
turbulence induced noise in the valve. A separate flame detector,
which may be a heat sensor, infrared or other optic flame detector,
or other type, may also be provided.
A tank level indicator may be formed as a linearly disposed array
of silicon diodes, for example 1N914 type. These diodes are held in
thermal communication with the tank, for example by a viscous
grease or temporary adhesive. The diodes are relatively matched, so
that a change in temperature will result in a measurable change in
characteristics. The diodes have a known temperature response
characteristic, and thus the temperature at each diode may be
measured. The tank level is determined by the point in the array at
which a significant temperature change occurs. Such significant
temperature changes will be seen while the tank is in use, and the
propane in the tank evaporating. When there is no temperature
change, such as with an empty or inoperative tank, a heating strip
may be provided over the sensing diodes which heats the wall of the
tank by a small amount. This temperature change is sufficient to
produce a significant response in the temperature sensing elements.
The heater excitation is then stopped, and the temperature sensors
monitored. Liquid propane through the wall will cool the wall
faster than gas, so the liquid level may be determined.
In the event of hazardous carbon monoxide or combustible gas levels
an audio and/or visual alarm may be created. If not corrected
within a reasonable period, the visual alert is ceased and the
audio alert operated in a pulsatile manner, in order to conserve
the battery. To indicate a low propane tank level, a differentiated
audio alert, such as a mild chirp, may be sounded.
It is therefore an object of the invention to provide a hydrocarbon
gas detector for use in unprotected environments having a low power
consumption and being suitable for extended, low maintenance,
battery operation.
It is a further object of the invention to provide an electronic
safety and control system for a barbecue or grill which enhances
the functionality and safety thereof.
These and other objects will become apparent from a review of the
detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with respect to the drawings,
in which:
FIG. 1 is a block diagram of a first embodiment of a hydrocarbon
gas sensing system;
FIG. 2 is a schematic diagram of a second embodiment of a
hydrocarbon gas sensing system;
FIG. 3 is a schematic representaition of a Fabry-Perot grating
laser diode hydrocarbon sensor embodiment;
FIG. 4 shows a schematic diagram of the microcontroller system
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a schematic drawing of an electronic device for
detecting a hydrocarbon gas. An infrared diode 1 produces an output
at about 1425 cm.sup.-1, which selectively passes through an
aperture 2 of an open cuvette 3 containing sample gas 4 or a closed
cuvette containing a reference gas 5, which, for example, has
propane at 25% of the lower explosive limit (LEL). After the
optical absorption of one gas 4, 5 is measured, the aperture 2
switches to the other position under power of a small solenoid 8,
and the optical absorption of the other gas 5, 4 is measured. The
sensor 7 is a silicon photodiode, which is sensitive in the range
of approximately 1200-1500 cm.sup.-1, which receives light from
both samples 4, 5, concentrated through a high infrared absorption
wedge 6. The output of the photodiode sensor 7 is amplified by an
amplifier 9 and digitized to 8-12 bits precision by an
analog-to-digital converter 10. A microprocessor 11 receives the
digitized signal, and processes it, using data stored in volatile
(RAM) 12 and non-volatile (ROM) 13 memory, to allow a comparison
with a normalized alarm threshold. An adaptive algorithm may be
used, employing parameters stored in volatile memory (RAM) 12 or
other writable memory. In event of an alarm condition, an audible
14 and visual 15 alarm is generated, through a driver circuit 16.
The system also includes a flame detector 17, which may be used to
alter detection thresholds, and a propane tank level detector
18.
The microcontroller program is stored in read only memory (ROM) 13.
The microcontroller 11 executes the program using temporary storage
in registers and random access memory (RAM) 12. Sensor calibration
data, as well as environmental factors and data about the propane
tank may be persistently stored and updated in writable memory, for
example RAM 13 or EEPROM (not shown). The microcontroller 11
preferably has an integral 10 bit analog to digital converter (ADC)
for reading sensor signals, and thus the microcontroller 11 and
analog-to digital converter 10 are integral. The analog-to-digital
converter may also be used to detect battery 20 condition through
battery output 21.
A system power controller 19 carefully limits power consumption of
the device to prolong battery 20 life. Thus, hydrocarbon gas
measurements may be taken every minute by powering up the sensor
(e.g., the light emitting diode 1, solenoid 8, detector 7 and
amplifier 9) for 1 mS for each of two measurements, between which
the system remains in a sleep mode.
The system preferably employs a sensor duty cycle of less than
about 25%, and more preferably less than about 5%, and still more
preferably less than about 1%. As is understood, the lower the duty
cycle, the lower the power consumption.
The electronic device is battery 20 powered, and is preferably
intrinsically safe, meaning that, even with a fault condition, it
will not be capable of igniting a combustible gas in the
environment. This intrinsic safety is achieved by the avoidance of
energy storage elements configured to provide spark energy to
ignite a flame, and through the use of flame arrestors (not
shown).
As shown in FIG. 2, the optical sensor may vary, for example,
including two infrared light emitting diodes 22, 23 with slightly
differing wavelengths, e.g., 1300 cm.sup.-1 and 1425 cm.sup.-1,
each separately driven by drivers 24, 25. These wavelengths
correspond to a peak absorption and adjacent low absorption region
for hydrocarbons. The output of the photodiode detector 26 is
converted into a differential signal by circuit 27, in the manner
of a correlated double sampling circuit, by amplifier 28 and
processed as in the system described with respect to FIG. 1, e.g.,
by an analog-to digital converter 10.
FIG. 3 shows yet another embodiment of an optical sensor. In this
case, a Fabry-Perot grating 30 on the surface of a 1425 cm.sup.-1
laser diode 31, which is coated with a material which selectively
absorbs hydrocarbons 32. The presence of the concentrated
hydrocarbons 33 in this surface layer 32 reduces the reflection
efficiency of the reflection grating 30 and thus increases the
lasing threshold of the laser diode 31. This threshold is measured
by a dynamic analysis of the startup transient.
FIG. 4 shows a schematic diagram of a microcontroller based system
40 which provides functionality and safety features for a barbecue
or grill.
The system provides a combustible gas sensor system 43 and a carbon
monoxide sensor system 41, which detect potentially hazardous
levels of these gases, as described above. In the event of
hazardous levels, an audible and/or visual alarm 51 is generated,
under control of the microcontroller based system 40. A flame out
detector 42 is also provided, which may also be used to generate an
audible and/or visual alarm 51, or alternately used to trigger a
relight of the flame by an igniter 56. The flame out detector 42
may also be used to alter an operational mode of the
microcontroller based system 40, for example, altering alarm levels
of the gas detectors 41, 43.
Advantageously, a tank propane level detector 45 provides an input
to the microcontroller based system 40, in order to alert the user
to low fuel level. An acoustic detector 48 senses the turbulent
flow of propane in the tank valve, tubing and burner (not shown)
and may be used to detect whether the barbecue or grill is "on".
Mechanical detectors 47 are also provided, which for example detect
the position of controls, such as propane control valves. The
propane controls may be electronic, with electromechanical valves
or the like employed to directly control propane flow based on the
mechanical detectors 47 or other user interface elements 46, or in
response to a control signal from the microcontroller based system
40.
A food temperature sensor 44 system may be provided to monitor or
control the cooking process. Barbecues and grills are often subject
to uneven cooking and subjective control over food preparations By
measuring food temperature with a food temperature sensor 44, the
cooking temperature may be monitored and/or controlled, to optimize
the time and/or temperature of cooking. For example, a "rare" steak
will optimally be cooked at a higher temperature for a shorter time
than a "well done" steak, with the optimal core temperature at
readiness of the "rare" steak below the optimum level of the "well
done" steak. Thus, the temperature-depth profile is controlled.
This profile may be controlled by a multisegment temperature
sensor, or based on various inferences, such as starting
temperature, food configuration, food density, and grill
characteristics and settings. Various foods, such as shellfish,
fowl, pork, lamb and beef, as well as vegetables, breads, and the
like, have differing optimal cooking temperatures, while the food
configuration will also influence the optimal time and temperature
profile with respect to depth. Therefore, in conjunction with the
food temperature sensor 44, the microcontroller based system 40 can
control the propane flow rate with the propane valve control 57. At
the determined end of food preparation, the microcontroller based
system 40 can turn off the propane to all or a portion of the
grill, and/or alert the chef by means of the audible and/or visual
alarm 51, user interface 54, through the network interface 55 to
other types of computing devices, or the like.
While the food temperature sensors 44 may be typical wired sensors,
such as thermistors, thermocouples, semiconductors, or the like,
these sensors may also be wireless encoded sensors, such as passive
surface acoustic wave sensors or encoded semiconductor sensors.
Therefore, a radio frequency interrogation system (typically a 900
MHz ISM band RF-ID system, not shown) may pole the individual
sensors to determine food temperature of different pieces or
portions of pieces. Since, in this case, the food temperature
sensors 44 are wireless, they will not interfere with cooking or
handling. Typically, these sensors will be reusable, although
disposable designs are possible. It is also possible to estimate
cooking by analyzing an infrared image of the top of the food,
which will be cooler than the bottom, cooking surface, and
generally the same or somewhat higher than the core temperature,
due to heat convection. Therefore, an infrared heat sensor or
imager may be provided for this purpose.
Since the microcontroller based system 40 is typically battery
operated, a low battery warning 53 is provided. Additionally, the
propane tank level may be indicated with a special propane tank
level output 52, and/or communicated through the user interface 54
or network interface 55.
The network interface 55 is preferably a 900 MHz wireless
communication system, and is preferably integrated with a wireless
radio frequency interrogation system for the food temperature
sensors 44, operating in the same frequency band. The
communications protocol is preferably TCP/IP, using hypertext
transport protocol (http). TCP/IP is a packet switched
telecommunications protocol, thereby allowing multiple devices to
simultaneously communicate through the same channel with addressed
data packets. The microcontroller based system 40 preferably acts
as an embedded web server, communicating information through the
wireless link and responding to commands and requests for
information. In this case, the user interface (input) 46 and user
interface (output) 54 may be virtualized or remote from the
microcontroller based system itself, and permit remote monitoring
and alarm indication. By employing a standard type communications
system, interoperability with separate systems is enhanced. In
order to reduce power consumption, the wireless communication
system may enter a low power mode when the barbecue or grill is not
in operation, for example broadcasting status and alarm conditions,
and otherwise being responsive to external systems, every five
minutes, and otherwise being inoperative. When the barbecue or
grill is in operation, the communications system is fully
operative, to provide short communications latencies. An external
communication may be used to fully activate the communications
system and network interface 55.
The network interface 55 communicates wirelessly with a base
station, which may be, for example, integrated with a home network
system, alarm monitoring system, or computer system. This base
station need not be dedicated to the microcontroller based system
40, and thus may be a generic wireless network device. In order to
power the microcontroller based system 40 during barbecue or grill
use, a thermoelectric converter may be provided to convert a
portion of the heat energy into electricity, using the
thermoelectric (Seebeck) effect. Alternately, a fuel cell may be
employed to extract hydrogen from the propane (e.g., during partial
combustion) to obtain electric power.
There has thus been shown and described barbecue and grill
electronic enhancement and safety systems, including
environmentally robust propane and hydrocarbon detectors adapted
for battery operation over extended periods, and methods which
fulfill all the objects and advantages sought therefor. Many
changes, modifications, variations, combinations, subcombinations
and other uses and applications of the subject invention will,
however, become apparent to those skilled in the art after
considering this specification and the accompanying drawings which
disclose the preferred embodiments thereof. All such changes,
modifications, variations and other uses and applications which do
not depart from the spirit and scope of the invention are deemed to
be covered by the invention, which is to be limited only by the
claims which follow.
* * * * *